Most cordless drills come with either a ½-inch or a ⅜-inch chuck. The size tells you two important things about a drill. First, it provides an upper limit for the shank size of the bits the drill can accommodate. Bigger bits often have wider shanks, so a heavy-duty paddle bit that you’d use for mixing grout or joint compound wouldn’t fit into a drill with a small chuck. Second, chuck size also tracks closely to a drill’s power and capability—more powerful drills usually have larger chucks and vice versa.

Early Li-ion batteries often needed to be charged and used under precise conditions to ensure peak performance. But the newest generation of batteries and chargers prevents overcharging batteries, alleviating the need to drain them fully between charges to ensure the longest possible life. New chargers also include an indicator light, which clearly displays how close the battery is to a full charge. Some brands also have indicator lights on the batteries themselves.

Li-ion batteries for cordless power tools have two important specs. Voltage correlates roughly to power. An 18-volt drill will be more powerful than a 12-volt drill from the same brand. But a 14.4-volt drill from one brand may be less powerful than a 12-volt tool from another. (Check out the power score in CR’s Cordless Drills ratings for a true comparison.) Amp-hours indicates how much fuel the battery contains, which translates to run time. A 4.0-amp-hour battery should run twice as long as a 2.0-amp-hour battery—but it’s also twice as heavy. And because some batteries charge in as little as 25 minutes, you might prefer two smaller batteries.

Brushless motors reduce friction and sense resistance from the work material, continually adjusting the amount of power they draw from the battery. Manufacturers say this translates to longer run times, more power, and a longer product life. In CR's cordless drill tests, the top six heavy-duty models all feature brushless motors, as does the top-performing general-use drill—the only 12-volt drill with a brushless motor tested. Warranties indicate manufacturers' confidence in brushless technology: three to five years on the new tool vs. just three for the older technology. We think that makes brushless a smarter buy.

Almost all cordless drills come with a built-in LED work light, a single Phillips bit, and extras such as belt clips and hard-sided cases. A few brands stand out for extra features. Milwaukee offers chargers capable of charging its 12- and 18-volt batteries at the same time—nice if you own a drill of each type. And Porter-Cable makes an LED flashlight that runs on one of its 20-volt batteries.